1) Field of the Invention
The present invention relates to a pumping light source having an amplification-band extending function for Raman amplification, capable of extending an existing amplification band stepwise while maintaining a flat amplification band, a Raman amplifier using the same, and a method and a program for setting an amplification band extension.
2) Description of the Related Art
An amount of information transmission has been increasing rapidly according to the spread of the Internet in recent years. To cope with this rapid increase in the amount of information transmission, an increase in a transmission capacity and an increase in a density of transmission of a transmission system are desired. As a method of expanding a transmittable capacity in a WDM system, there is a method of extending a signal band. As a conventional technique for extending a gain wavelength band of a Raman amplifier used in the WDM system, there is a method of extending the gain wavelength band from a wavelength band of about 1530 nanometers to 1565 nanometers called a C band to a wavelength band of about 1565 nanometers to 1625 nanometers called an L band. This is a method of extending the gain wavelength band from the C band to a (C+L) band at a time (see, for example, Japanese Patent Application Laid-Open No. H10-73852 and Japanese Patent Application Laid-Open No. 2001-15845).
However, when it is unnecessary to extend an amplification band to be larger than a required amplification band, there is a problem in that excess capital investment is performed. In some cases, it is desired to extend an amplification band little by little while controlling initial investment and collecting capital investment costs. In the market, the advent of a flexible Raman amplifier, which is capable of extending a flat amplification band by an extension unit smaller than that in the past, has been demanded.